Exhaust gas emissions from internal combustion engines may be reduced through the use of exhaust aftertreatment devices such as catalytic converters located in the exhaust system.
The operating efficiency of a catalytic converter may be temperature dependent and a catalytic converter or, to be more precise, the catalyst brick forming the active part of the catalytic converter may reach a minimum temperature (light-up/off temperature) before effective conversion of the exhaust gases occurs. This minimum temperature may be equal to a temperature in a region of 350 to 400° C. There is therefore a finite time during which the catalyst temperature will be below this minimum temperature following a cold engine start during a warm-up period. During this warm-up period the exhaust gas hydrocarbon emissions out of the engine may be high and it may be desirable to heat the catalyst to its minimum efficient operating temperature (the light-off temperature) as quickly as possible.
Previous attempts to rapidly raise the temperature of a catalytic converter following a cold start may include supplying more fuel to the engine which can be by way of applying an additional load to the engine by, for example, recharging batteries or other energy storage devices which will also increase the temperature of the exhaust gas flowing from the engine or increasing the engine idle speed to an artificially high level. Another option to reduce the time needed to reach the light-off temperature is to directly inject fuel just prior to or directly into the aftertreatment device itself which combusts and thereby may increase the temperature within the aftertreatment device.
However, the inventors herein have recognized potential issues with such systems. As one example, the above heating operations include inefficient operating conditions because the fuel consumption of the vehicle will be high during this mode of operation and such approaches will result in an unacceptably high fuel penalty.
It is an object of this disclosure to minimize the time taken for a catalytic exhaust aftertreatment device to reach light-off during an engine warm-up period by rapid heating of the aftertreatment device while minimizing any associated fuel penalty.
In one example, the issues described above may be addressed by an emission control system having an electronic controller, an electrically controllable actuator operable in response to a control output from the electronic controller and a catalytic aftertreatment device connected to an exhaust outlet from an engine, the catalytic aftertreatment device comprising a housing defining an inlet flow passage, an outlet flow passage and a chamber in which is located a catalyst and a flow control device positioned upstream from the catalyst, the flow control device comprising inner and outer exhaust gas flow passages linking the inlet flow passage to the catalyst and a flow regulating means to selectively vary the flow of exhaust gas through the outer exhaust gas flow passage wherein the electrically controllable actuator is connected to the flow regulating means to limit the flow of exhaust gas flowing through the outer exhaust gas flow passage to speed up light-off of the catalytic aftertreatment device following a cold start up of the engine. In this way, a portion of the catalyst may be rapidly heated during the cold start up of the engine.
As one example, the flow regulating means may comprise one of a number of vanes and a number of flaps rotatable from a first position in which substantially no exhaust gas can flow through the outer exhaust gas flow passage to a second position in which there is substantially no restriction to the flow of exhaust gas through the outer exhaust gas flow passage. The outer gas flow passage may be an annular exhaust gas flow passage. The flow regulating means may comprise a number of vanes and the vanes may be spaced circumferentially around the annular exhaust gas flow passage. Each of the vanes may be arranged to rotate about a respective pivot axis that extends radially outwardly from a longitudinal axis of the catalytic aftertreatment device. The vanes may be linked together by a linkage mechanism so as to be moveable in unison between the first and second positions. The linkage mechanism may have an input member for connecting the linkage mechanism to a common actuator. The electronic controller may be arranged to move the vanes to the first position when it is desired to speed up light-off of the catalytic aftertreatment device and move the vanes to the second position when light-off has occurred. The system may further comprise at least one of an exhaust gas temperature sensor and an exhaust gas emission sensor to provide an indication to the electronic controller when light-off has occurred. The electrically controllable actuator may be connected to the input member of the linkage mechanism. According to a second aspect of the disclosure there is provided a motor vehicle having an emission control system constructed in accordance with said first aspect of the disclosure. According to a third aspect of the disclosure there is provided a method for reducing the time needed for a catalytic aftertreatment device forming part of an emission control system constructed in accordance with said first aspect of the disclosure that is connected to receive exhaust gas from an engine to reach a light-off temperature, wherein the method comprises establishing whether an engine start-up is a cold engine start up and if the start-up is a cold engine start-up using the electrically controllable actuator to control the flow regulating means to restrict the flow of exhaust gas through the outer flow passage so as to speed up light-off of the catalytic aftertreatment device.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.